It is known that one of the ways to combat airline saturation (and the associated disadvantages such as busy periods at airports, the noise near such airports, etc.) is to increase the carrying capacity of the aircraft.
Of course, for an improved-capacity transport aircraft such as this to be successfully commercially operable, it is essential that its operating costs be lower than the sum of those of the aircraft it is supposed to replace. In particular, its fuel consumption needs to be modest, which means that its mass and drag need to be measured and that its propulsion system needs to be relative frugal.
American U.S. Pat. No. 4,165,058 already discloses an improved-capacity transport aircraft comprising two parallel fuselages with a front lower wing supporting the front lower parts of the two fuselages and a rear upper wing supported by the rear upper parts of those fuselages.
An aircraft such as this has the advantage of having a structure that is particularly robust because it is able to withstand bending moments. What this means is that its mass can be relatively low by comparison with the total mass of two aircraft each having one of the fuselages. By contrast, the aerodynamic effect that the front lower wing has on the rear upper wing generates a great deal of induced drag, especially since the lift generated by each of said wings is preferably the same. In an attempt to avoid such excessive drag, this American U.S. Pat. No. 4,165,058 makes provision for moving the rear upper wing up away from the fuselage by raising it up on very tall vertical struts. This then leads to a loss of flexural rigidity of the structure, to excessive vertical size and, in all probability, to the aircraft being difficult to fly because of the ensuing high position of the center of gravity.
Furthermore, it is known that, for the same propulsive power, the fuel consumption of a turboprop engine with at last one propeller is far lower (of the order of 15% lower) than that of a turboshaft engine. It would therefore be advantageous, in aircraft, to replace turboshaft engines with turboprop engines. However, turboprop engines have the disadvantages firstly of requiring a large ground clearance because of the propeller or propellers with which they are equipped, and secondly of requiring steps to be taken to prevent debris from said turboprops or the propellers thereof from damaging or even destroying said aircraft should such turboprops or propellers break. Of course, such steps are generally expensive both in terms of cost and in terms of weight.